I. Field of the Invention
This invention relates generally to the manufacture and use of balloon tipped angioplasty catheters and more particularly to a means for facilitating the initial purging of air therefrom prior to their introduction into the vascular system of patients.
II. Discussion of the Prior Art
As an alternative to coronary bypass surgery, a procedure referred to as transluminal angioplasty has become increasingly popular because it is significantly less traumatic than the open-heart surgery required for a coronary bypass operation. As is explained in the Schjeldahl et al. U.S. Pat. No. 4,413,989, in carrying out transluminal angioplasty, an elongated flexible catheter having a balloon or expander member at its distal end is introduced at an appropriate location in the vascular system and then routed through the vascular system to the particular coronary artery, which has been found to be partially occluded by fatty deposits or other types of stenotic lesions. Once the catheter is in place and the expander member is properly positioned relative to the lesion, fluid, under relatively high pressure, is introduced into the lumen of the catheter and it flows into the expander member and inflates same so as to force open the occluded vessel.
In the initial stages of the surgery, upon removal of the balloon tipped catheter from its sterile package, it is necessary to purge the air from the catheter prior to its introduction into the patient. This is necessitated by the fact that, if air (a compressible fluid) is trapped in the catheter, the balloon cannot be inflated to an appropriate working pressure. Also, when inflated with a radiopaque marking liquid, the presence of air in the balloon may result in an error in the accurate positioning of the expander relative to the lesion being treated. Thus, it has been the practice to repeatedly fill and aspirate the catheter with a liquid, such as saline solution, in such a way such that the air in the catheter tends to be mixed and entrapped in the liquid and drawn out of the catheter.
Attempts have also been made to provide a small air passage in the balloon so that air can be forced out through it, but this has not been altogether successful because when the liquid is again aspirated and withdrawn from the balloon to cause the balloon to collapse and assume its low profile state prior to being introduced into the patient, air can again be drawn through that same tiny orifice and the purging step is effectively defeated. Other purging protocols have required that, following the inflation of the expander member and the elimination of air from the interior of the catheter and its distal balloon by inflation with saline, the balloon be dipped in a tray of sterile saline solution as the liquid is again aspirated from the catheter. The immersion of the balloon into the pan of saline solution prevents air from re-entering the catheter through the tiny port in the distally located balloon.
Cardiovascular surgeons have complained about the difficulty attendant in purging the catheter of its air prior to use. The aforementioned procedure is time consuming and requires additional equipment to be located in the operating room setting which is generally already somewhat crowded with surgical apparatus. Accordingly, it would be advantageous to provide a balloon tipped catheter for use in angioplasty procedures wherein the catheter can more conveniently be purged of air prior to its introduction into the patient's vascular system. It is accordingly a principal object of the present invention to provide such a catheter.
Another object of the invention is to provide an angioplasty catheter having an air pervious, liquid impervious unidirectional vent in the wall of the expander mounting tube which permits the egress of entrapped air during the purging operation but which becomes sealed and blocks the subsequent inflow of air as the purging liquid is aspirated from the catheter.